Field devices such as, for example, level meters, pressure gauges and flowmeters are extensively utilized in various areas of today's industrial life in order to determine measured values in tanks or tubes. The measured values are transmitted to control or management centers by means of different data transmission technologies. In this case, the analog and the digital radio transmission on the basis of electromagnetic waves is one preferred means, for example, for forwarding levels determined by a corresponding sensor in the field to the central office.
If part of the transmission is bound to electrical lines, the measured value to be forwarded is transmitted with the aid of an electric current in accordance with the two-wire or four-wire technique. This measuring current that is output, for example, proportionally to the physically existing measured value in a current loop may be used for a safety function in a safety-relevant monitoring circuit under certain circumstances. In this case, a deviation between the actually generated measuring current and the applicable nominal value that corresponds to the actually existing physical measured value may occur for various technical reasons. One reason for such a deviation may be, for example, the failure of a component in a current-defining network.